Monday, May 16, 2011

Dolly launches with tail

Dolly launches. I have limited experience with them and I don't like them. Of course, you'll think, you're writing this after Julia's incident. But Jamie, Dave and others at Quest will know I've expressed my preference for foot launches before. And I've written about my concerns about dolly launches with the tail before. So why am I writing about it now? Because I have pictures of my tail and because I am reflecting on my first serious series of dolly launches. Of course the second reason may well be triggered by the incident.So why don't I like them?First of all, because they introduce a number of risks. I feel comfortable foot launching and my hang gliding instructor, Tom Haagdorens, always told me to keep things simple if possible. And I think that is a really good advice. Don't get me wrong, dolly launching is a matured way of launching. The risks are well known and there are procedures to deal with them (check AOA, check for loose wires, check connection to tow cable, use weak links, …) Still, I prefer not to have to deal with those risks at all. Of course I have to deal with the risks involved in foot launching. That includes not tripping and stabilizing the glider while running. But these are the things I'm used to deal with and I feel I have more control over those.So, first of all, I want to keep it simple. Next to that, I feel uncomfortable when the glider is rolling on the dolly on a grass field. There are always bumps, sometimes quite violent bumps. My base bar is not made for that, I don't feel what the glider is doing anymore because I am having a real firm grip, the glider is getting a beating (think about the A frame, the harness, the jesus bolt and so on) and I don't want that. It was revealing to have 2 launches from the runway during the race and rally. I felt what the glider was doing then. I had no doubt about when to leave the dolly. I felt comfortable with the situation then.And, the dollies are not made with gliders with tails in mind. People told me not to worry about that. Just make sure you leave the dolly late, when the glider is flying and there will be more than enough clearance for the tail. I never felt comfortable with the "do not worry" advice. And as it turned out, the day before Julia's incident, my tail got stuck to the dolly pretty badly (see the picture below). I always left the dolly late, made sure my keel had left the dolly. Yet, my tail got stuck for what seemed to be 2 to 3 seconds. I was happy to feel it launch after all, looked back and saw that the tail was partly disassembled. I immediately released and landed to check the damage. Alex rolled me back into the line after I made sure the tail was fixated again and seemed to be in good order.

We know that the dolly may jump up when the rear wheel hits a bump. I am quite convinced that that caused my problem that day. But I have no eye-witnesses…What I know is that dollies are not designed for tails. If the tail gets caught by the keel suspension, it will not release because of the forward force applied to the glider and the backward angle of the keel suspension. You might think that we could solve that problem by making sure that the suspension is tilted forward, but that is not true. If that would be the case, a tail hitting the suspension would rise and thus possibly introduce negative pitch with a bad crash as the result.The best solution I've seen so far are dollies with just a minor V-shaped cut-out for the keel. But you can imagine the glider to jump out of that on a bumpy field.So, please do take care when launching with tails on dollies. I always put the AOA as high as I can, knowing that this makes me more vulnerable to crosswinds. But I need to clear the dolly with the tail. So, now you know why I feel uncomfortable with the situation. Even with a high AOA, which you don't want to have for safety reasons, I have the safety issue of maybe not clearing the dolly with the tail. In the future, I'll ask to do foot launches if the terrain we're launching from is bumpy.